Inductors



vMay 27, 1958 w. F. GLOVER ETAL 2,836,804

INDUCTORS Filed Feb. 16, 1955 2 Sheets-Sheet 2 Inventors W. F. G L OVE R 0. H5O EN By Attorney United States Patent INDUCTORS William Frank Glover and Douglas Hiley Owen, London, England, assignors to International Standard Electric Corporation, New York, N. Y.

Application February 16, 1955, Serial No. 488,632

Claims priority, application Great Britain February 23, 1954 7 Claims. (Cl. 336-135) This invention relates to electric inductor units of the kind providing for a marginal adjustment of the inductance after manufacture.

It frequently happens, for example in telecommunication circuits, that a final marginal adjustment of the inductors is required after a circuit has been assembled and connected. This is particularly true of filter circuits. In any case the facility of adjusting the inductance over a narrow range means that the manufacturing tolerances can be easier which results in greater ease and reduced costs in manufacture.

The inductors to be described are of the iron-clad kind in which a winding on a suitable former surrounds a central core, usually cylindrical, of magnetic material and in which the magnetic circuit is completed by further external portions of magnetic material substantially completely surrounding the winding and central core.

Such an inductor is described in the application of Glover and Giles, Serial No. 392,408, filed November 16, 1953, now abandoned. In the present application the cores are made of non-metallic magnetic materials of very high resistivity known as ferrites. The magnetic structure is made in two major parts, preferably identical in size and shape which fit together to provide the cylindrical central core and which are formed with disc shaped portions extending over the flat surfaces of the former carrying the winding. The magnetic circuit is completed by a cylinder of magnetic material surrounding the former and in magnetic contact with the said two disc shaped portions.

The central cylindrical portions of the two major parts are brought close together to form the central core of the magnetic structure but are separated by a small air gap lying nearly but not quite along a plane at right angles to the axis of the central core.

The complete magnetic structure and winding are carried inside a high conductivity metal case to provide electro-magnetic shielding and mechanical protection. This case has a cylindrical side wall, a circular base and a detachable circular cover. The side wall and base are preferably made of brass to ensure rigidity with high conductivity while the detachable cover is made of a resilient high conductivity material such as beryllium copper. One of the major parts of the core is attached to the base of the case and the other major part is attached to the cover. ,When the cover is in place on the case the two parts of the core are separated by a small gap and the shape of this gap can be varied by rotating the cover, thus varying the inductance. Means is provided for restraining the movement of the cover so that the adjustment once made will not be altered by vibration. The leads from the winding are brought out through a slot in the Wall of the case and may be attached to terminals carried on a block mounted on the exterior of the case.

According to the permeability of the core and the number of turns of the winding, the inductance can be varied over a very wide range. By a suitable selection 2 of core material the electrical losses due to hysteresis and eddy currents can be controlled to have a very low value.

The permeability of a ferrite is determined by its composition and the heat treatment and other processes to which it has been subjected during manufacture. Similarly the hysteresis factors can be controlled by the composition treatment. It follows that by suitable selection of the ferrites used the desired permeability can be obtained and a maximum figure for the losses ensured.

The permeability of a ferrite varies with temperature. In the present construction it is possible to make the two major parts of the magnetic structure of a ferrite with a positive coefficient of permeability with temperature change, and to make the surrounding cylinder, which completes the magnetic circuit, with a negative permeability temperature coefiicient without there being any significant difference between the permeabilities of the major parts and the cylinder, thus an overall permeability largely independent of frequency can be secured.

As the coeificient of thermal expansion of the high conductivity case may be as much as ten times that of the ferrite, and as the two major parts of the ferrite structure are respectively attached to the base and to the cover of the case, it can be seen that the air gap between the two parts of the core would vary with temperature changes. This variation would lead to serious changes of the inductance of the unit, and in order to avoid this, the lid of the case is made of a corrugated resilient metallic material and the unit is so constructed that the air gap remains constant in spite of changes of temperature. The two major parts of the structure are of such dimensions that when they are pressed against the surrounding cylindrical portion the desired small air gap is obtained.

The invention therefore provides an adjustable inductor unit in which two parts of a magnetic ferrite core are relatively rotatable to adjust the dimensions of an air gap therebetween and in which each of said parts is secured to a corresponding portion of a metal case Within which said inductor is housed, the said portions of the said metal case being relatively rotatable for the said purpose.

The invention further provides an adjustable inductor unit comprising a Winding surrounding a substantially cylindrical central core made of a magnetic ferrite which core comprises two parts separated by a relatively small air gap lying about a plane inclined at a small angle to a plane perpendicular the axis of said cylindrical core each of said core parts being firmly secured to a corresponding portion of a metal casing surrounding said core and said winding, the two portions of said casing being capable of rotation with respect to one another about the axis of said cylindrical core whereby the inductance of the inductor unit is adjustable.

An embodiment of the invention will now be described with reference to the accompanying drawing in which:

Fi 1 represents a plan view of an inductor unit according to the invention;

Fig. 2 represents an elevation of the same inductor unit partly in section;

Fig. ,3 represents a side elevation of the same inductor unit showing the terminal plate;

Fig. 4 represents a detail of the casing of the inductor unit.

The complete inductor unit consists of the magnetic core and the winding all enclosed Within a metal casing. In Fig. 1 there is shown the cover 10 which is mounted on the cylindrical wall 11 of the casing, as shown in Fig. 2. The cover 10 which is of a resilient metallic material, such as beryllium copper, is corrugated, as shown at 12 in Figs. 1 and 2. The cover is also provided with a rectangular indentation 13. The base 14 of the casing is welded to the side Wall 11 and is also inductor unit on a plate or panel.

provided with an indentation corresponding to indentation 13 in the cover 10. The base 14, unlike the cover 10, is not corrugated. After the side wall 11 has been welded to the base 14 the lower part 16 of the magnetic structure is cemented to the base 14. The lower part 16 of the structure is provided with a slot 17 which engages the indentation 15 in the base 14. The former 13 made of a suitable insulating material and carrying the winding 1.9 is then placed in position on the lower part 16 of the magnetic structure and cemented thereto.

A hollow cylinder 21} of magnetic material is placed in position to surround the former in and winding 19 and is cemented to the lower part 16. The lead 21 is passed through an aperture 22 in the cylinder 24} and through a further aperture 23 in the casing wall 11 and is attached to one of two terminals 24 mounted on a terminal plate 25 which is mounted on the wall 11 of the casing. The lead from the other end of the coil is brought out similarly and attached to the second terminal on plate 25. The terminal plate 25 and terminals 24 can be seen in Fig. 3. The terminal plate 25 can conveniently be held in position by two lugs 26 pressed out from the casing wall 11 and passing through narrow slots in the terminal plate 25.

The upper part 27 of the magnetic core is cemented to the detachable cover 10, the slot 28 in the part 27 engaging the indentation 13 in the cover.

A circumferential groove 29 is pressed in the rim 30 of the cover it} and a clip 31 consisting of a circular springy piece of wire is pressed into the groove 29. The clip is shown in Fig. 4. A short slot 32 is cut through the rim 3% of the cover it to communicate with the groove 29. This slot accommodates an outwardly bent portion 33 of the clip 31 to restrain the circlip from rotation in the groove 29.

A circumferential groove 34 is pressed in the upper portion of the wal ii of the casing to correspond with the groove in the rim 30 of the cover 10, and when the cover is pressed onto the casing the clip 31 will enter into both the grooves 29 and 34 and Will hold the cover in position. The cover it} is made of somewhat resilient metal, such as beryllium copper, and the corrugations ensure that, When the cover is in position on the outer wall 11 of the casing, the upper part 27 of the magnetic structure is firmly pressed against the upper surface of magnetic cylinder 29 thus ensuring that the air gap between portions 16 and 27 is kept constant. It will, however, still be possible to rotate the cover 10 with respect to the casing against the friction of the clip 3i on the surface of the groove 34 in the side wall 11. As explained above this alters the shape of the air gap between the two portions of the core. In Fig. 2 the two planes bounding the air gap are parallel, but if the cover were rotated through 180 the shape of the cross section of the air gap would be triangular. The flux will therefore become concentrated towards those parts of the core portions which are nearest together and the increase of flux density in and near those parts will more than offset the rather small reduction in the remoter parts of the air gap so that the inductance of the unit will be increased. By correctly proportioning the several variables: permeability, width of gap, and angle of slope of the adjacent faces of the core portions, a variation of inductance of about plus or minus 5% can readily be obtained at any inductance value of the wide range of inductances for which such inductors are suitable, and at the same time the hysteresis factor can be held within 110%.

In Fig. 1 there are shown feet for mounting the These feet are presed out from the base plate 14 as indicated in Fig. 3.

While the principles of the invention have been described above in connection with specific embodiments,

and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What we claim is:

1. An adjustable inductor unit comprising a metal casing formed of two cooperating parts of circular cross section, spring means for releasably attaching said parts together while permitting relative rotation thereof, a magnetic core formed of two parts positioned coaxially within said casing, each part having an extended flange at one end and a substantially'fiat surface at the other end which is at an angle with respect to a plane perpendicular to the axis of said casing, said parts being positioned in said casing with said surfaces facing each other but separated to form an air gap, an induction coil surounding said magnetic core and between said flanges, a sleeve of magnetic material surrounding said coil and between said flanges, said sleeve acting to maintain said gap when said core parts are urged towards each other, means between each core part and its adjacent casing part for causing rotation of Sai Casing part to cause rotation of said core part, and resilient means for urging said core parts towards each other.

2. An adjustable inductor unit, as defined in claim 1,

. in which the two parts of the casing telescope one within the other and the spring means for releasably attaching said parts comprises a wire ring of spring metal, the inner telescoping part of said casing having a circumferential groove in its outer surface to receive said ring and the outer telescoping part of said casing having a circumferential groove in its inner surface to receive said ring, whereby said casing parts may be snapped together, and in which the means between each core part and its adjacent casing part for causing rotation of said casing part to cause rotation of said core part comprises a noncircular depression in one of said parts and a cooperating non-circular extension on the other part, and in which the resilient means for urging said core parts toward each other comprises circular corrugationson the end wall of one of said casing parts.

3. An adjustable inductor unit, as defined in claim 2, in which the sleeve of magnetic material has approximately the same permeability as the two' core parts but is of such composition that its coefiicient of change of permeability with temperature compensates for the equivalent coefiicient of said core parts to maintain the gap between said core parts constant with variations of temperature.

' 4. An adjustable inductor unit, as defined in claim 3, in which the magnetic material of the core and sleeve is a ferrite.

5. An adjustable inductor unit, as defined in claim 3, in which the casing is made of high-conductivity metal.

6. An adjustable inductor unit, as defined in claim 1, in which the magnetic material of the core and sleeve is a ferrite.

7. An adjustable inductor unit, as defined in claim 1, in which the sleeve of magnetic material has approximately the same permeability as the two core parts but is of such composition that its coefiicient of change of permeability with temperature compensates for the equivalent coefficient of said core parts to maintain the gap between said core parts constant with variations of temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,439,809 Hunter Apr. 20, 1948 FOREIGN PATENTS 417,378 Great Britain Oct. 1, 1934 442,849 Great Britain Nov. 19, 1934 

